The invention relates to a process for the partial combustion of finely divided solid fuel, such as pulverized coal, in which the latter is introduced together with oxygen-containing gas via a burner into a reactor space. The invention further relates to a burner for use in such a process for the partial combustion of finely divided solid fuel.
Partial combustion, also known as gasification, of a solid fuel is obtained by reaction of the solid fuel with oxygen. The fuel contains as useful components mainly carbon and hydrogen, which react with the supplied oxygen--and possibly with steam and carbon dioxide--to form carbon monoxide and hydrogen. Depending on the temperature, the formation of methane is also possible. While the invention is described primarily with reference to pulverized coal the process and burner according to the invention are also suitable for other finely divided solid fuels which can be partially combusted, such as lignite, pulverized wood, bitumen soot, and petroleum coke. In the gasification process the oxygen-containing gas may be pure oxygen or an oxygen-containing gas such as air or a mixture of air and oxygen can be used.
There are, in principle, two different processes for the partial combustion of solid fuel. In the first process, solid fuel in particulate form is contacted with an oxygen-containing gas in a reactor in a fixed or fluidized bed at temperatures below 1000.degree. C. A drawback of this method is that not all types of solid fuel can be partially combusted in this manner, which limits the flexibility of the method. High swelling coal, for example, is unsuitable since particles of such a coal type easily sinter with the risk of clogging of the reactor. In some cases the high yield of methane obtained with this type of process is a disadvantage.
In a more advantageous process finely divided solid fuel is passed into a reactor at a relatively high velocity. In the reactor a flame is maintained in which the fuel reacts with oxygen-containing gas at temperatures above 1000.degree. C. Contrary to the first gasification method, the residence time of the fuel in the reactor is in this method relatively short, in any way short enough to prevent sintering of the solid fuel. The last mentioned method is therefore suitable for the gasification of a relatively wide range of solid fuels.
In the latter process the solid fuel is usually passed in a carrier gas to the reactor via a burner, while oxygen-containing gas is also passed via the burner to the reactor. Since solid fuel, even when it is finely divided, is usually less reactive than atomized liquid fuel or gaseous fuel, great care must be taken in the manner in which the fuel and oxygen are mixed. If the mixing is insufficient, zones of underheating are generated in the reactor next to zones of overheating, caused by the fact that part of the solid fuel does not receive sufficient oxygen and another part of the fuel receives too much oxygen. In zones of underheating the fuel is not completely gasified, while in zones of overheating the fuel is completely converted into less valuable products, viz. carbon dioxide and water vapor. Local high temperatures in the reactor have a further drawback in that damage is caused to the refractory lining which is normally arranged at the inner surface of the reactor wall.
A primary requirement for obtaining a sufficient mixing of the solid fuel with oxygen throughout the gasification process is a stable supply of solid fuel to the burner fuel outlet. The supply of solid fuel should, moreover, be uniformly distributed over the total fuel outlet, whereas oxygen-containing gas should be supplied uniformly to the flow of solid fuel, to generate an intimate and uniform contact of oxygen with the solid fuel.
Further care should be taken to prevent damage to the burner front caused by the heat load during the gasification process. To protect the burner front from overheating it is necessary to prevent premature contact near the burner front of the supplied oxygen with already formed carbon monoxide and hydrogen in the reactor, which contact would result in a hot flame front at the burner front.